Corvo is pretty much perfect if you enjoy finding your birds and marvelling at the chaos wrought by inclement weather. It might seem the island presents a blissfully easy way to bag Yankee rares; in order to provide some balance, I feel duty bound to outline those facets of the experience that might not sit comfortably with one and all. Therefore, prepare yourselves for... the dark side [cue rhythmic pounding of timpani or discordant blast of brass].
1. The lack of common migrants. A bit of a double-edged sword this one. On the one hand, it is quite easy to spend six hours with nothing more to trouble the retinas than Blackcap, Chaffinch and Blackbird; the flip-side is that, by becoming accustomed to every call, squeak and fart emitted by the regulars, one day you'll find yourself chasing an unseen bill-snap through the canopy knowing full well you are just about to nail something very exciting indeed.
2. The distinct possibility of breaking one's neck. The sides of the ribeiras are steep, coated in a reddish clay-like sediment (that goes all Bon Jovi after rain), and littered with decrepit stone walls with an unerring ability to collapse at the least useful moment. One day someone will have a serious accident in one of those valleys. If Corvo doesn't get you in a single fatal blow, the sheer physical grind of birding an upturned cone of petrified volcanic rage is sure to wear you down in the end. The only sizeable area of almost flat ground is the platform on which the village perches, beyond that, it is all gradient: caldera and cones, radial faults and basaltic dykes, they are all a bit 'upsy-downsy'.
3. Extreme weather. Another example of the double-edged weaponry which litters the rarity finding battlefield. Every year we beseech the ornithological gods for another hurricane season like 2005, we sit under anticyclones hoping for a storm so big it destroys another city, we revel in the increasing frequency of extreme weather events (keep burning the carbons folks) but, one day, a blow will come through that will rip the roof off the Comodoro, or a perfect storm that'll pluck a birder from the crater's rim and deposits them, head first, into the top of a Cryptomeria and we'll all wish we'd been botanists.
4. Travel woes. You pretty much have to like flying in planes big and small; on my last journey home I had five flights (this must be one of the few places you can do this and remain in Europe). Changing flights can be something akin to [well you think up something that should be straightforward but is inexplicably impossible]. Also, if the wind is coming from the wrong quarter the flight is cancelled; if the wind is out of the north there'll be no discussion, no chance and no plane.
5. Mental fatigue. Finding small birds in big valleys choked with sub-tropical secondary growth is tiring. Each day's toil erodes the cerebral defences, consumes the mental reserves and chips away at your belief in the redemption promised by the big one. The creeping, then rampant, agoraphobia; the rushing wings of the Corvo wraiths, at first, just perceptible in the depths of the darkest ribeira, become, by the end of a ten day stay, a constant, hounding cacophony. Crushed birders cower at the foot of walls, grazed flesh pressed against unforgiving alkaline basalt; gently rocking, their eyes white, wide, wild. The thrashing canopy closes in, the 'chink, chink' of aggravated finches piercing tympanic membranes, the 'tack, tack' of insistent Blackcaps tearing along shredded auditory nerves to explode in clusters on the superior gyrus of your, now crumbling, temporal lobe. And finally, there you are, trapped in a verdent 'Scream' or stumbling through a 'Guernica' of Atlantic Gulls and shattered windmills. Quietly violent, unbearably intense, unreal; this is birding in the foaming maw of an Atlantic breaker of existential anguish,...
...nothing that a cuppa and a slice of Rosa's chocolate cake can't put right mind :-)
Missing the flyby Double-crested Cormorant proved too much.
PS. I didn't even mention the limited diet - ham & cheese anyone?